Pacing of the left side of the heart (i.e., left ventricle and/or left atrium) has been used, e.g., to improve cardiac function in heart failure patients. A challenge with such left side pacing is that undesirable extracardiac stimulation often occurs, especially of the diaphragm and/or the phrenic nerve.
The left phrenic nerve, which provides innervation for the diaphragm, arises from the cervical spine and descends to the diaphragm through the mediastinum where the heart is situated. As it passes the heart, the left phrenic nerve courses along the pericardium, superficial to the left atrium and left ventricle. Because of its proximity to electrodes used for left side pacing, the phrenic nerve can be inadvertently stimulated by a pacing pulse. Such phrenic nerve stimulation and/or more direct stimulation of the diaphragm can result in involuntary contraction of the patient's diaphragm, which can be similar to a hiccup, and annoying to the patient. Other types of inadvertent extracardiac stimulation that may occur include stimulation of the patient's pectoral muscles overlying implanted electrodes.
When implanting a left ventricular and/or atrial lead, physicians are faced with the limitations of the cardiac venous anatomy. Additionally, physicians are often faced with a potentially mottled ventricular myocardium for achieving adequate pacing and sensing thresholds. Further, physicians should also ensure that the implanted lead does not unacceptably stimulate extracardiac structures. If the lead does result in unacceptable extracardiac stimulation, then mechanical repositioning typically needs to be performed, which can be time consuming and costly. Accordingly, it would be advantageous to reduce the probability of undesirable extracardiac stimulation caused when attempting to pace the left side of the heart.